1. Field of the Invention
The present invention relates to the processing of wafers for the semiconductor industry, and more particularly to processes for the elimination of voids in solder on that wafer.
2. Prior Art
The electronics industry utilizes semiconductor wafers in the production of very large scale integrated circuits (VLSIC) and ultra large scale integrated circuits (ULSIC) for chips and the like. Those semiconductor wafers go through a wide variety of manufacturing standard processes in order to produce a perfect semiconductor product.
One process for such wafers comprises a flux reflow for screen printing solder wherein solder paste is printed onto the surface of a semiconductor wafer through a screen mask. That wafer is then placed into a reflow furnace to begin further processing. The furnace heats the wafer therewithin, to a point above the solder melting temperature. The solder is thus melted with the flux during that reflow process. That melting results in the production of a flux vapor, air, processing gas and other gaseous components which may be trapped inside of the molten solder. Such gaseous components may form voids within the solder “bumps” on the wafer. It is this step that may result in the production of the voids which are generated and left to contaminate the solder on the wafer. That wafer is thus subsequently processed through a photoresist film removal step. The wafer then goes through a conventional flux coating process before a second reflow operation begins. The wafer is then placed into a conventional reflow furnace with controlled nitrogen therein, the sample wafer being heated to above the solder melting temperature again, to produce a final formation of bumps on the wafer, leaving coated flux residues thereon. The wafer sample then in a further step, goes through a conventional chemical and mechanical washing to remove those flux residues. A final step, comprises the wafer sample going through a conventional drying process before a final inspection. The wafer with its circuit thereon, and the solder bumps thereon, may contain a lot of voids in that solder, which voids are undesirable for optimum wafer utilization.
Such voids within the solder bumps reduces production yield and ultimately minimizes device reliability. Other disadvantages of these prior art wafer treatments is the high cost of flux and deflux chemicals. In this traditional source of production for wafers in the semiconductor industry, the equipment to produce such wafers has a large footprint which leads to a high cost of capital equipment and a unnecessarily high cost clean room. Further disadvantages include environmental hazards created by the chemical treatment required herein.
It is an object of the present invention to overcome the disadvantages of the prior art.
It is a further object of the present invention to provide a wafer processing operation which simplifies the steps required by reducing the number of those steps necessary to produce a satisfactory semiconductor wafer.
It is a further object of the present invention to provide a wafer processing operation which is more environmentally friendly than the prior art.
It is a further object of the present invention to provide a wafer processing operation which is more economical to run that the prior art, both in size of the apparatus for completing the steps and for minimizing the cost of materials.